A printing unit is known from DE 44 30 693 A1. A double printing group, consisting of two transfer cylinders forming a print position and the associated forme cylinders, can be driven by a common drive motor. A transfer cylinder can be brought into two positions, a print-on and a print-off position, by the provision of eccentric seating.
EP 0 862 999 A2 discloses a double printing group in which the two transfer cylinders, which together form a print position, are not in a driven connection with each other. Instead, each has a drive motor together with the associated forme cylinder. In addition to on and off positions, the two transfer cylinders can be brought into a third position in relation to each other, in which third position, a web can be passed between the two transfer cylinders during the printing operation.
A device for putting cylinders into contact is known from DE 44 01 289 A1. Besides an out of contact position of the cylinders, it is possible with this device to set two different contact positions of the cylinders in relation to each other for different thicknesses of the web of material. In this case, a support element having two different stops is provided for the setting.
DE 93 11 113 U1 shows a double printing group through which a web of printed material can be guided, in a contactless manner, in a print-off position. The contactless passage is achieved by the use of guide rollers which are arranged upstream and downstream of the print position.
In DE 198 03 663 A1 the intention is to maintain, if possible, a print position during a flying plate change. This is achieved, inter alia, by use of a forme cylinder which can be driven independently of the associated transfer cylinder. During the plate change, the transfer cylinder continues to work as a counter-pressure cylinder, together with the web, and is in a driven connection with the counter-pressure cylinder.
U.S. Pat. No. 5,265,529 discloses cylinders which can be brought into three different positions. The various end positions can be adjusted, with respect to the contact position, in accordance with defined paper thicknesses etc. by the use of adjusting devices. Stops limit the contact path toward the others cylinders.
A drive mechanism for a printing unit is known from DE 198 53 114 A1. By the introduction of intermediate gear wheels into a drive train, the gear wheel engagement in the drive mechanism is independent, to a large extent, of the position of the cooperating cylinders.